A conventional coded signal editing apparatus and edited coded signal decoding apparatus, particularly for use in video editing, is currently available in the market. This type of coded data editing apparatus is capable of creating a new image by rearranging a current image for a specified frame. It is also capable of creating a new image by properly connecting specified frames of a plurality of video signals.
FIG. 1 is a block diagram showing a coded data editing apparatus for editing baseband video signals. FIGS. 2(a) through 2(e) are timing charts for explaining the operation of a conventional coded data editing apparatus. FIG. 2(a) shows an input image signal A. FIG. 2(b) shows a time base adjusted form of the input image signal A. FIG. 2(c) shows an input image signal B. FIG. 2(d) shows a time base adjusted form of the input image signal B. FIG. 2(e) shows an edit output (signal change-over output) from the coded data editing apparatus.
Referring to FIG. 1 and FIGS. 2(a) through 2(e), the input image signal A, as shown in FIG. 2(a), is applied to an input terminal 1 in units of frames, i.e., frames Am, Am+1, Am+2, etc. successively. The input image signal B, as shown in FIG. 2(c), is applied to an input terminal 2 in units of frames, i.e., frames Bn, Bn+1, Bn+2, etc. successively. The input image signal A is applied to a buffer memory 3 and a sync separator 4 while the input image signal B is applied to a buffer memory 5 and a sync separator 6. The sync separators 4 and 6 separate sync signals from the input image signals A and B and apply the sync signals to write controllers 7 and 8, respectively. The write controllers 7 and 8 control the writing operations to buffer memories 3 and 5 using the sync signals of the input image signals A and B for storing the input image signals A and B in buffer memories 3 and 5, respectively.
Readout of data from buffer memories 3 and 5 is controlled by a readout controller 9. This readout controller 9 controls the readout of data stored in buffer memories 3 and 5 based on a reference signal given from a reference signal generator 10. As a result, the input image signal A is read from buffer memory 3 after being delayed by .DELTA.TA and the input image signal B is read from buffer memory 5 after being delayed by .DELTA.TB, as shown in FIGS. 2(a) through 2(e). The time delays .DELTA.TA and .DELTA.TB synchronize input image signal A and input image signal B, respectively, with the reference signal. That is, the data read from buffer memories 3 and 5 are synchronized by the reference signal, and the frames Am', Am+1', etc. of the time base adjusted input image signal A are read out at the same rate as the frames Bn', Bn+1', etc. of the time base adjusted input image signal B, as shown in FIGS. 2(b) and 2(d).
The image signals read out of buffer memories 3 and 5 are applied to terminals a and b, respectively, of a switch 11, as shown in FIG. 1. Switch 11 selectively switches between terminals a or b by a change-over control signal that is applied through a terminal 12. For example, assume that the switch 11 has initially selected the terminal a and the output is the frames Am', Am+1', etc. based on the input image signal A. Once a change-over signal is applied through terminal 12, switch 11 will switch from terminal a to b in response to the change-over control signal at the change-over point between frames Am+2' and Am+3', etc. of the input image signal A, as shown in FIG. 2(e). After this change-over point, the switch 11 transmits the output from buffer memory 5 instead of buffer memory 3 and, as shown in FIG. 2(e), the frames Bn+3', Bn+4', etc. based on the input image signal B become the new output.
Since the base band video signals A and B have been synchronized prior to the change-over, the frames Am+2' and Bn+3' are output consecutively. Also, in this case it is also necessary to take the phase of a color subcarrier into consideration.
In recent years, a system for recording or transmitting image information by encoding at high efficiency has been of great interest. A proposed system is described in Japanese Patent Application Tokkai-Hei 4-14974 entitled "Moving Picture Coded Data Recording Method", which discloses an editing apparatus for editing high efficiency encoded (compressed) video signals in the as-coded state. In this prior art device, coded data for a moving picture is obtained by quantizing an input image signal after it is intra-frame coded or interframe coded. Moving picture coded data is edited in units of frame groups by defining a frame group as a specified number of frames and setting an edit flag for a frame group immediately after an edited group. The sequence of coded frames is changeable by detecting this edit flag.
The coded quantity of high efficiency coded data per frame differs depending on its pattern and on whether the encoding method is intraframe compression or interframe compression. Accordingly, for editing high efficiency encoded video signals, it is essential that the time bases of the frames before and after the change-over point are the same. In the proposed system described above, editing and decoding in units of frame groups is possible when high efficiency coded video signals are changed over (edited) for each frame by adjusting the time bases of the frames to agree with each other.
However, the above-mentioned system discloses a apparatus for editing only one video signal. With the increasing adoption of interframe compression for high efficiency encoding in addition to intraframe compression, decoding may become impossible when an edit is performed between two input image signals A and B. Interframe compression is a method using the interframe correlation, and only the differential value between the preceding and the current frame images is transmitted. Accordingly, a decoding result from a preceding frame is needed for decoding intraframe compression signals. However, when compression data of a specific frame of the input image signal A is changed over to interframe compression data by adjusting the time bases of both data to agree with each other, this interframe compression data cannot be decoded because there is no preceding frame image signal of the interframe compression data for input image signal B.
Further, when transmitting signals in units of packets, editing high efficiency coded signals and decoding editing signals may become difficult. FIGS. 3 and 4 are timing charts for explaining this problem.
FIG. 3(a) shows that a video signal is transmitted in units of packets, i.e., packets A-1, A-2, A-3, etc. FIG. 3(b) shows the video signal frames V-0, V-1, V-2, etc. included in the packets, as shown in FIG. 3(a). Each packet has a fixed word length, as illustrated by the solid vertical lines in FIG. 3. Each frame has been encoded in variable length and its coded quantity varies for each frame.
Now, it is assumed that the input image signal A is transmitted in units of packets, i.e., packets Am+1, Am+2, Am+3, etc. The boundaries between the frames am+1, am+2, am+3, etc. included in these packets are shown with broken lines in FIG. 4(a). Further, it is also assumed that the input image signal B is transmitted in units of packets, i.e., packets Bn+1, Bn+2, Bn+3, etc The boundaries between the frames bm+1, bm+2, bm+3, etc. included in these packets are also shown with broken lines in FIG. 4(b).
When an input image signal is transmitted in units of packets in this manner, the boundaries of video frames are unclear and consequently editing in units of video frames is difficult. Even if the boundaries of frames are clear, editing can be difficult. For example, when connecting frame am+2 of the input image signal A with frame bn+4 of the input image signal B, the boundary between these frames is between packets Am+3 and Bn+4, but when frame am+2 is connected to frame bn+4, subsequent packets must be prepared to transmit frames after this connection point at a fixed word length.
Therefore, it is necessary to edit in units of packets. FIG. 4(c) illustrates an example where packet Am+3 is connected to the packet Bn+4. After packets Am+3 and Bn+4 are connected, the edited data contains unnecessary parts AO and BO, which are the first half of the frame am+3 and the latter half of the frame bn+3, illustrated by the shadowed portions in FIG. 4(c). When decoding the output C after editing, all the unnecessary parts AO and BO from the point Ap in FIG. 4(c) are decoded after frames am+1 and am+2 are decoded. That is, after the video signals corresponding to the first half of the frame are decoded, the decoding of the unnecessary part BO of the next packet Bn+4 begins. However, it is unclear which part of frame bn+3 is the leading portion of the unnecessary part BO and which part is the data of the unnecessary part BO. Furthermore, it is uncertain whether the decoding process was properly carried out and disturbance of the final image is expected at this portion.
Further, the same problem exists in the editing of recorded signals in a VTR. FIG. 5 is a drawing for explaining this problem.
The recorded quantity on each recording track of a magnetic tape is fixed but data quantities of the video frames am+1, am+2, etc., and bn+1, bn+2, etc. are not fixed. Therefore, the boundary between video frames can lie at any position on a track, as shown in FIG. 5. Accordingly, when video signals of the tracks Am+3 and Bn+4 are connected to each other, the unnecessary part, as illustrated by the shadowed portion in FIG. 5, is produced. Even when the boundary between the frames am+2 and bn+4 is clear, removal of the unnecessary part is required by recoding data in the middle of the track, and it is usually impossible to remove the unnecessary part except in special cases. Consequently, a disordered image is produced on a reproduced image because of this unnecessary part.
As described above, when interframe compression signals were edited, the image became disordered as the interframe compression signals (a differential image signal) were decoded using a predictive original image signal that was not related to the interframe compression signals. In addition, when video signals recorded or transmitted in fixed word lengths of packets, etc. were edited, the image also became disordered when decoding the video signals.